Since wood is light, strong, and can be easily processed or shaped, wood has been used from old for building materials, furniture materials, and other wide uses but has a disadvantage that wood is liable to cause dimensional deformation by the increase or decrease of bound water in the wood. Also, wood which is used for outdoor materials such as outdoor wall materials, ceiling materials under the eaves, sliding shutters, etc., is liable to be deteriorated by ultraviolet rays in sun beam, moisture, oxygen, etc., and thus has a problem in weather resistance.
For improving the dimensional stability and the weather resistance of the aforesaid wood, the inventors previously proposed a process of modifying wood by dipping wood in a mixed solution composed of a polybasic acid anhydride and an epoxy compound to cause reaction under heating, whereby the wood is chemically modified by adding the polybasic acid anhydride to the hydroxyl groups of the wood component by a ring-open esterification reaction to form carboxyl group and at the same time by adding the epoxy compound existing in the mixed solution to the carboxyl groups formed at the side chains.
The modified wood obtained by the above-described process is excellent in dimensional stability, weather resistance, etc., but in the case of producing such woods in an industrial scale, there are following problems. That is, since a mixed solution composed of a polybasic acid anhydride and an epoxy compound is used at high temperature in the aforesaid process, the stability of the solution in the long run is poor and hence it is difficult to use the solution continuously for a long period of time. Also, there is a disadvantage that wood components are partly dissolved in the mixed solution in a high-temperature reaction to cause discoloring of the wood. Furthermore, there is a disadvantage that a large heat energy and a long time are required for raising the temperature of the mixed solution.
Also, a problem to be solved in the aforesaid production process of modified wood is that in the case of washing the wood which was finally treated in the mixed solution under heating, the treated wood contains the unreacted mixed solution in an amount of from about 50% by weight to 200% by weight of the wood and hence it is a loss in industrial view point to remove the mixed solution by washing. Furthermore, in this case, there is also a disadvantage that a large amount of organic solvent is used for washing the treated wood, which is undesirable in the points of safeness and working environmental sanitation.